Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$45.89	8.704%	$49.8843	$49.88	$49.90	$49.90
Purchase #2	$139.37	6.342%	$148.2088	$148.21	$148.20	$148.20
Purchase #3	$136.89	13.144%	$154.8828	$154.88	$154.90	$154.90
Purchase #4	$198.74	9.148%	$216.9207	$216.92	$216.90	$216.90
Purchase #5	$76.73	11.459%	$85.5225	$85.52	$85.50	$85.50
Purchase #6	$244.90	9.346%	$267.7884	$267.79	$267.80	$267.80
Purchase #7	$54.84	6.246%	$58.2653	$58.27	$58.25	$58.30
7 purchase totals =	$897.36		$981.4728	$981.47	$981.45	$981.50